Idaho Road Network

By | October 13, 2022

Idaho has a fairly thin road network, especially in the central part of the state, where there are only two main US Highways, US 93 and US 95. There is only one road in the southwest. Interstate 15 forms a north-south route in the east of the state, and Interstate 84 forms a diagonal east-west route in the southwest of the state. Interstate 86 forms a short east-west route in the east of the state, between I-84 and I-15. In the north of the state, where the state is at its narrowest, Interstate 90 crosses the state. Most major towns are on or near these highways, except Rexburg, Moscow, and Lewiston.

Road management

The state highway authority is the Idaho Transportation Department, abbreviated ITD. ITD manages 8,022 kilometers of road and 19,765 kilometers of lane kilometers. The state also operates 1,824 bridges. ITD is one of the smaller departments of transportation in the United States in terms of number of ways in the administration of the state, especially given its large geographic size.

The ITD has its origins in the State Highway Commission that was established in 1913. In 1919, this merged into the Department of Public Works, which was reorganized in 1950, forming the Idaho Department of Highways. In 1974, it was renamed the Idaho Transportation Department, emphasizing that the state was responsible for more than just roads. At the time, the Department of Transportation was renamed as such in many states.

  • Bittranslators: State overview of Idaho, including geography, economy, population and history as well as introduction to major cities of Idaho.

Interstate Highways

Idaho is served by four main routes of Interstate Highways. Notably, the state has no highway connection between the north and south of the state. The main highway for traffic within Idaho is I-84. The I-90 is mainly important for through traffic. I-86 is quite short and serves traffic almost exclusively within Idaho. I-15 handles both through and regional traffic.

I-184 is a spur of I-84 in the capital city of Boise. Highways in Idaho almost always have 2×2 lanes, except in the Boise region, where I-84 has up to 2×4 lanes. This is the state’s only busy corridor.

  • Deluxesurveillance: Nickname of Idaho as The Gem State. Also covers geography, history, economy, politics and administration of the state.

US Highways

The US Highways handle regional traffic. The roads in southern Idaho have a somewhat striking course and are regularly double-numbered with each other and Interstate Highways. Partly due to the I-84/86 corridor, the US 20 and US 26 have relatively little importance for through traffic. US 20 has more importance in eastern Idaho and is a divided highway and part freeway from Idaho Falls to Yellowstone National Park. US 26 provides access to the Jackson Hole region of western Wyoming. US 93 is the primary connection between Idaho and Nevada, although US 95 is also used by traffic to Nevada, passing through Oregon. coming. US 95 is also the primary connection between north and south Idaho. US 2 is mostly double-numbered in northern Idaho with US 95. US 95 is also the primary connection to Canada. Other US Highways, such as US 12, US 30, US 89 and US 91 have a more secondary importance.

State Highways

In Idaho they speak of a ‘state highway’. In written language, a road number is usually represented as ‘SH-1’, with a hyphen. Idaho’s road network is not very dense, and the major routes are U.S. Highway or Interstate Highway. The network of state highways in Idaho is relatively small. Almost all state highways have one or two digits, there are only a few state highways with three digits. In addition, numbers are frequently skipped.

In the 1920’s the major roads of Idaho were lettered by Charles B. Sampson of Boise, with A through Y, the so-called ‘Sampson Trails’. This system was replaced in the 1930s by a numbered network of state highways.


Most of Idaho’s highway network was built in the 1960s. As early as 1974, all Interstate Highways in Idaho were completed except for a missing link of I-90 in Wallace, which was not opened to traffic until 1991.

Former road numbers

Some Interstate Highways were originally numbered differently. I-84 was numbered as I-80N until 1980, and I-184 in Boise was numbered as I-189N. The I-86 was originally presented as the I-82N, but has been numbered as the I-15W for some time. Until 2013, I-86 was the shortest east-west route of the major Interstate Highways routes in the United States. In Texas, the I-2 was subsequently assigned, which was shorter.

Idaho Road Network